Radon dosimeter



Nov. 1, 1966 E. L. GEIGER 3,283,153

RADON DOS IMETER Filed July 2, 1963 5| INVENTOR ERIC L. GEIGER United States Patent 3,233,153 RADGN DQEsKMlETER Eric L. Geiger, Santa Fe, N. Mex, assignor to Eberline Instrument Corporation of Santa Fe, N. Mex. Filed July 2, 1963, Ser. No. 292,322 7 (Claims. (Cl. 250-83) This invention relates to physical well-being and more particularly to radiation monitoring, especially of individuals.

Radioactive properties of various substances have been known for more than half a century, including the presence of radioactivity in forms described as alpha, beta and gamma rays. Instruments for detecting and determining the strength of radioactivity have been produced. Badges for personal wear consisting of light-tight compartments for sensitized film on which various rays produce paths which may be made visible have been used.

Radioactive elements disintegrate or undergo change in their physical form to form daughters or other elements, over a period of time. Thus, there have been found to exist in nature three series of radioelements known as the uranium, thorium and actinium series. These naturally occurring elements are constantly decaying or undergoing disintegration into other elements within the series.

Exposure of the person to the rays from radioelements may produce harm, depending upon the strength or intensity of the rays and the length of time of exposure and the area of the body affected. Thus, a high intensity field may be experienced for only a brief time without apparent harm, whereas a low intensity field may be experienced for a longer time.

Persons working in areas in which radioactive materials are present have used film badges, previously described. These badges are checked from time to time and indicate the amount of radiation to which the badge has been exposed. Such badges indicate primarily the exposure to gamma radiation and have a window through which incidental beta radiation may be received.

Radioactive material may exist in deposits or may be air-borne and thus be contained in the dust to which we are exposed and which we breathe. Furthermore, one of the forms in which the rad'ioelements occur in the disintegration process is a gas known as radon. Radon gas tends to disintegrate in a short time, its disintegration product or daughter being known as polonium. Polonium similarly disintegrates in a short time and characteristically tends to deposit on the surface of any adjacent material. Such tendency of polonium to deposit or attach itself to a physical structure is viewed as presenting an unusual hazard to breathing organisms, including man, since the polonium may tend to deposit itself within the body during breathing and accumulate over a period of time. Thus, the body would become a carrier of radioactive elements whose radioactivity would persist for a substantial period of time.

Such hazard is believed to be higher than that from naturally occurring radioelements existing in other portions of any of the series which do not tend so readily to attach themselves to physical matter, as in the case of the radon daughter polonium. For example, other radioactive substances may be present in the air which we breathe and may be exhaled after being in the body a short time and without tending to collect or attach themselves to the body. Such substances, even if not inhaled, but deposited on the body, may be removed by washing and decontamination procedures. However, the depositing of polonium within and on the body is believed to present increased hazard because of the difliculty of decontaminating the body, especially its internal surfaces.

Due to the extent of the hazard from polonium, the

desirability of a monitoring device by means of which the element can be detected is apparent. Since polonium is the first radon daughter, the detection or monitoring of radon provides an indication of the hazard from polomum.

Accordingly, it is an object of the present invention to provide a detector or dosimeter from radon and radon daughters.

A further object is the provision of a dosimeter especially adapted for wear by individuals in a space where hazardous concentration of radioactive products of radon and radon daughters may be encountered for indicating the exposure of an individual to such products in the space.

These and other objects of the invention will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is an exploded assembly drawing of a device constructed in accordance with the present invention, and a clip for carrying such device;

FIGS. 2, 3 and 4, sections on the lines 2-2, 33 and 4-4, respectively;

FIG. 5, a side elevation illustrating the assembly with the cover raised; and

FIG. 6, an illustration of a manner of wearing the device.

With further reference to the drawing, the device includes a base 10 having a cover 11 and a frame 12 disposed within the base beneath the cover. For the purpose of mounting the device on the person, a holder or clip 14 may be used. However, the holder is not a required element of the invention.

The base 10 is substantially rectangular and has a central recess 15, upstanding left and right flanges 16, 17 which project above the walls of the base defining the recess 15 and a central cavity 19 in the floor of the base. Bores 20 extend from the two side walls and one end wall 21 of the base into the cavity 19. These bores may be of various sizes and number. A total of fifteen, each having a diameter of A of an inch, has been found to be satisfactory. The purpose of these bores is to permit the passage or diffusion of radon gas present in the air into the base and into the cavities 19 and 15.

In order to shield any light received through the bores from reaching sensitized material, to be described, the frame 12 is mounted within the recess 15 and carries a thin film of Mylar material having an aluminized coating. The coated film prevents the passage of light through the frame but is of such thinness (e.g. .00025 inch) that the passage of alpha particles therethrough is not appreciably impeded.

The cover 11 has an inner recess 25 within which a backing plate 26 is mounted. The backing plate is relatively soft and preferably formed of a plastic such as neoprene. A sheet of film F is positioned within the frame just above the aluminized Mylar and is held in flattened position as a result of engagement with the backing member 26. The film is positioned with its emulsion side down or adjacent to the Mylar window.

The space beneath the aluminized Mylar window and the upper surface of the base permits the gases received within the chamber 19 to diifuse over the entire surface of the window in order that the film may be subjected to alpha particles over the entire space instead of only within the restricted outer confines of the recess 19.

The cover 11 is pivotally mounted on the base between the flanges 16, 17 by pins 28 located in bores 29 at the ends of the cover and having their reduced extremities 30 urged outwardly by springs 32 into holes 31 near the ends of the flanges 16, 17. The cover may, if desired, be separated by pressing inwardly on the ends 30 of the pins. The cover is retained in closed position against inadvertent opening by a latch 34 consisting of a pin having an enlarged head 35 with a bore 36 for receiving the stem 37 of a latching element having a head 38 positioned in a bore 39 of the base. The stem 37 of the latching element is urged into the bore 36 by a spring 40 retained in the bore by a screw 41. From the side of the base opposite that in which the latching element is mounted a bore 43 is provided through which a thin rod (not shown) may be inserted to retract the stem 37 from the bore 36 of the latch 35 in order to permit disengagement of the latch from the latching element. The upper portion or stem 44 of the latching element is of reduced diameter and permanently connected to the cover by suitable means such as spreading the extremity into engagement with the surfaces defining the bore 46 of the cover.

If desired, a hollow rivet 48 may be placed in the cover overlying the backing pad 26 for the purpose of securing the pad or plate in position within the cavity.

To protect the parts against corrosion and to reduce the possibility of light leaking into the interior, the base, the cover and the window framework are preferably etched and black anodized.

In order that the device described may be conveniently worn on the person, a holder 14 is provided. The holder has a base portion 50, side retaining members 51 and an attaching lobe 52. The side members have flanges 53, 54 presenting a means for retaining the device in secure position and openings 55 positioned to expose the ends of the bores 20 in the side wall to the exterior.

In use the device is worn by the miner or other individual for a definite period of time, such as a week. A portion of the radon to which he is exposed diifuses through the holes 20 into the central cavity. A portion of the radon atoms disintegrate, forming the daughter polonium and alpha particles having kinetic energy. The polonium atoms tend to deposit on the surface of the inner cavity and subsequently to disintegrate by each emitting an alpha particle. Some of the alpha particles from the disintegrating radon and polonium atoms pass through the Mylar window into the alpha-sensitive emulsion of the film and produce alpha tracks in the emulsion which can be observed with a microscope after the film has been processed. The number of alpha tracks observed per unit of film area is related to the total exposure of the miner to radon. Thereby an indication of the miners exposure to the hazard from radon and radon daughters is provided.

It will be obvious to one skilled in the art that various changes may be made in the invention without departing from the spirit and scope thereof and therefore the invention is not limited by that which is illustrated in the drawing and described in the specification, but only as indicated in the accompanying claims.

What is claimed is:

1. A dosimeter for radon and radon daughters of a size adapted to be worn on the person, comprising a fiat base having a recess in its central portion,

a multiplicity of small bores extending outwardly from the periphery of the recess in a plurality of directions to the exterior of the base, whereby circulation of air into and out of said recess is facilitated,

a light-tight window mounted above the recess, said Window being opaque to visible light and sufiiciently thin to permit substantially unimpeded passage of alpha particles, and

a removable cover over the window on the side opposite said recess and mounted to define a space for a sheet of film containing an alpha-sensitive emulsion capable of producing permanent visible indications of the presence and the number of alpha particles striking the film.

2. The invention of claim 1, said recess having a broad portion underlying the window and a reduced cavity adjacent thereto, said bores extending to said cavity.

3. The invention of claim 2, the depression being substantially circular and substantially smaller than the recess.

4. The invention of claim 1, said cover being pivotally mounted at one end and having latching means at the other.

5. The invention of claim 4, said latching means including a pin with an enlarged head received in the base and having a bore therethrough, a latching element positioned in a bore in the base and having a reduced extremity receivable within the bore of the latching element, means urging the reduced extremity into said bore, and said pin being connected to said cover.

6. The invention of claim 1, and a film backing member mounted in the cover.

7. The invention of claim 1, and a holder for the dosimeter for attaching it to apparel, said holder having openings for exposing the outer ends of the bores.

References Cited by the Examiner UNITED STATES PATENTS 2,562,969 8/1951 Teichmann 250-83 X 2,706,939 4/1955 Fairbank 25083 X 3,056,886 10/1962 Glaude et al. 25083.6 X

RALPH G. NILSON, Primary Examiner.

ARCHIE R. BORCHELT, Examiner.

Disclaimer 3,283,153iEric L. Geiger, Santa Fe, N. Mex. RADON DOSIMETER. Patent dated Nov. 1, 1966. Disclaimer filed Apr. 6, 1970, by the assignee, E berlz'ne Instrument Corporation. Hereby enters this disclaimer to claims 1 and 4 of said patent.

[Ofioial Gazette November 10, 1970.] 

1. A DOSIMETER FOR RADON AND RADON DAUGHTERS OF A SIZE ADAPTED TO BE WORN ON THE PERSON, COMPRISING A FLAT BASE HAVING A RECESS IN ITS CENTRAL PORTION, A MULTIPLICITY OF SMALL BORES EXTENDING OUTWARDLY FROM THE PERIPHERY OF THE RECESS IN A PLURALITY OF DIRECTIONS TO THE EXTERIOR OF THE BASE, WHEREBY CIRCULATION OF AIR INTO AND OUT OF SAID RECESS IS FACILITATED, A LIGHT-TIGHT WINDOW MOUNTED ABOVE THE RECESS, SAID WINDOW BEING OPAQUE TO VISIBLE LIGHT AND SUFFICIENTLY THIN TO PERMIT SUBSTANTIALLY UNIMPEDED PASSAGE OF ALPHA PARTICLES, AND A REMOVABLE COVER OVER THE WINDOW ON THE SIDE OPPOSITE SAID RECESS AND MOUNTED TO DEFINE A SPACE FOR A SHEET OF FILM CONTAINING AN ALPHA-SENSITIVE EMULSION CAPABLE OF PRODUCING PERMANENT VISIBLE INDICATIONS OF THE PRESENCE AND THE NUMBER OF ALPHA PARTICLES STRIKING THE FILM. 